In some vehicles, such as hybrid vehicles, a high level system controller may control a plurality of power and/or torque sources for propelling the vehicle. For example, the controller may allocate a total drive request among the various sources in different ways depending on operating conditions.
In one example, one factor considered by the controller in allocating the request among the various sources is the available output range of an individual source. For example, an engine may have a variable maximum torque output depending on operating conditions, and it may further change as the engine ages. Thus, if the range varies differently from the predicted range, the allocation made by the controller may result in the engine operating at less than its peak output, or providing less output than the controller requests. Such operation can affect vehicle performance and fuel economy. Further still, if the engine is over-taxed, it may provide insufficient vacuum for various conditions, such as fuel vapor purging.
The inventors herein have recognized that a range of the available maximum engine torque can be accurately estimated based on engine operating conditions. In one embodiment, a method for operating a powertrain in a vehicle is provided. The powertrain includes an electric drive and an internal combustion engine. The method comprises providing torque to drive the vehicle from both the electric drive and the engine, where engine torque is varied within an allowable range; and when operating the engine at an edge of the range, adjusting the range based on whether a selected operating condition can be provided by the engine. In this way, it is possible to more accurately allocate the propulsion torque among the hybrid vehicles various sources, and thereby achieve improved vehicle operation. In one particular example, it is possible to adaptively adjust the available engine output torque range to the vehicle operating conditions and account for production variation, engine aging, etc.